(a) Technical Field
The present invention relates to an alumina-coated spinel-silicon carbide refractory composition with high resistance to slag penetration and a method for manufacturing the same, which is used for a coal gasifier because of its high corrosion resistance and resistance to slag penetration.
(b) Background Art
A coal gasifier is an apparatus that enables to economically and cleanly produce useful compounds from low-grade coal. A mixture of gases obtained from the process is called synthesis gas, mostly consisting of CO and hydrogen. In a reactor, being a core of the coal gasifier, oxygen and water are added to a material containing carbon and heated at a high atmospheric pressure of about 30 to about 60. The heating temperature ranges from 1,300 to 1,600° C. depending on the melting point and the viscosity of the coal slag. Accordingly, a refractory brick used as a lining material inside the reactor requires good resistance to thermal shock, corrosion, erosion, and slag penetration. Due to the extremely strict requirements on refractories in the coal gasifier, many studies have been reported that only the refractory brick with high chromia content can meet these requirements.
The refractories having high chromia content are being used for the coal gasifier due to their high resistance to slag penetration. High-chromia refractories are very expensive, and chromia, a hazardous material under environmental regulation, may be evaporated. There is a continuing need for improved refractory, particularly with respect to slag penetration, and preferably for the development of a chromia-free refractory. U.S. Pat. No. 6,815,386 B1 relates to a refractory used for an Integrated Gasification Combined Cycle (IGCC) gasifier, in which the content of chrome oxide (Cr2O3) is equal to or greater than 60 wt %.
Examples of the chrome-free refractories include Al2O3, MgO, spinel-based (MgAl2O4), and SiC. Regarding alumina-based refractories, there are a steel-making refractory (U.S. Pat. No. 4,326,040) including alumina by 85 wt % and carbon, and a refractory (US 2009/0227441 A1) including alumina by 40 wt % to 60 wt % with fine silicon carbide powder, and using aluminum phosphate binder. Regarding MgO-based refractories, there are a refractory (US 2007/0213199 A1) including MgO by 55 wt % to 95 wt % and ZrO2 by 3 wt % to 20 wt %, a refractory (U.S. Pat. No. 4,849,383) including MgO and CaZrO3, and an MgO-spinel refractory (Japanese Patent Application Publication Hei 6-100347). Spinel-based refractories have in general (US 2007/0042896 A1, US 2008/0254967 A1) good resistance to high alkaline environment. As silicon carbide-based refractories that are widely used in steel making, there are silicon carbide-alumina refractory (U.S. Pat. No. 5,318,932) with alumina by 10 wt % and silicon carbide refractory (US 2006/0281625 A1) bonded by silicon nitride.
It is known that the refractories described above are lower than high chromia refractories in corrosion resistance against coal slag at a temperature of 1,500° C. or higher and under high pressure. In order to develop a chrome-free refractory for a coal gasifier, the present applicants developed a method of manufacturing a non-chrome refractory with good resistance to thermal shock, corrosion, and slag penetration by using alumina surplus spinel and silicon carbide as refractory materials, adding fine alpha alumina and alumina precursor, and performing heat treatment to form a bonding between the refractory materials and alpha alumina generated by the phase transition of alumina precursor (Korean Patent Application Publication No. 10-2011-0083705). However, in the spinel-silicon carbide refractory developed, since the surface of the silicon carbide particles was not fully protected by fine alumina powder, some fine gaps were found at the interfaces due to a reaction between spinel and SiC. Also, it was found that the fine gap causes penetration of low viscous slag at a high temperature. The present applicants made efforts to eliminate the small gaps generated at the interface between the large spinel aggregates and the silicon carbide matrix in the spinel-silicon carbide refractory. As a result, a spinel-silicon carbide refractory in which there is no noticeable gap between the aggregates and the matrix has been invented by using spinel aggregates coated with submicron-sized alumina particles.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.